Electrical sound-reproducing apparatus



Sept. 6, 1927.

1,641,664 DE FOREST v v v ELECTRICAL SOUND REPRODUGING APPARATUS Filed July 1, 1922 2 Sheets-Sheet 1 IIIIUIIID ATTORNEYS Jim 1.

Se t. 6 1927.

p DE FOREST ELECTRICAL SOUND REPRODUCING APPARATUS Filed July 1, 1922 2 Sheets-Sheet INVETOR BY ATTORVNEY 5 k.

Patented Sept. 6, 1927.

wires STATES PATENT orrics- LEE DE FOREST, 0]? NEW YORK, N. Y., ASSIGNOR, IBY MESNE. ASSIGNMENTS, TO' DE FOREST PHONOFILM CORPORATION, OF JERSEY CITY, NEW JERSEY, A CORPORA- TION OF DELAWARE.

ELECTRICAL SOUND-REPRODUCING: APPARATUS.

Application filed July l,

This invention relates to electrical sound reproducing apparatus. The object of the invention is to provide an electrically controlled sound reproducer tive arrangement of parts, all as will be more fully hereinafter-set forth, as shown by the accompanying drawings, and finally pointed out in the appended claims.

' Referring to the drawings,

Fig/1 is'an enlarged diagrammatic V ew of an arrangement illustrating my lnventi on. Fig. 2 is a partially diagrammatic View and partially in section showing the reproducingmechanism of my invention.

Fig. 3 is 'a similar view of-a modified arrangement embodying my invention.-

Fig. 4 is a view of a pol element employed in accordance with my invention.

"Figs. 5, 6 and 7 are views similar to Fig. v1

. illustrating diagrammatically further modified arrangements embodying my invention.

The same part is designated by the same reference numeral wherever itoccurs throughout the several views.

In my Patent No. 1,299,356ygra1ited to me April 1, 1919 I disclosed my original discovery that between an open air glower,

for example, a 'Nernst burner, or from an oxide coated platinum filament or strip, and a coldconducting member placed near to said glower and made electrically positive frelat'ive thereto, an electronic and ionic current passed. Furthermore, that such a de- 5 vice could be made tooperatevery much as does myaudion, or three-electrode vacuum,

tube (United States Patent, No. 879,532),as a detector or amplifier (and consequently therefore as-an oscillator) provided a third or control electrode, preferably in the form of a grid, be introduced into the space between the hot cathode and cold anode, and

the three element'sbe then connected in the usual audion circuits.

tion of electrode 1922. Serial N0. 572,174.

I have also discovered that these ionic made to increase or decrease, the surround; ing air-expands or contracts, and this with no perceptible time lag, so thatif a power- :ful telephonic current be impressed upon the external anode-cathode circuit a clear and'exact reproduction in sound'waves inthe air surroundingthe cathode is obtained. I have here therefore a novel and Valuable means for reconverting' telephonic currents into sound waves, and one which can be employed not merely as a new type of telephone receiver, but as a loud speaker, en-

tirely devoid of diaphragm of any description, and therefore capable of sound reproduction of practically perfect fidelity. In Fig. 1 I show a plan View of such a device as I have described, together with the elemental circuits-involved. I have found that considerable areas of cathode and anode elements placed very close together are necessary to give the required degree of action in the surrounding, or between-lying,

air, to produce sounds of the desired intensity. Accordingly I prefento use a great length of filament or strip. preferably wound in a spiral form, as the cathode, and

a corresponding length of anode strip, interwound with said cathode close to but insulated from the same. uch cathode strip can very conveniently be made of fine woven wire for example, of platinum, or mol bdenum, or nichrome, wire, as shown in ig. 4. The longitudinal wires l'carry the oathode heating current, and the transversewires 2 being'interwoven merely to bind and support the heating. Wires' 1. To render.

such heated cathode strip far more active for the purpose of electronic emission, I prefer to fill the meshes of the wire gauze thus formed with certain oxides of the rare earths, or with oxides of barium, strontium,

-or calcium, which have for years been employed to coat the cathodes in Wehnelt.

tubes and oxide-filaments audions. Such material is indicatedat 3, Fig.4. In place of this wire mesh I may employ a thin strip of platinum or tantalum, or the like, simi larly coated with electronic material.

InFig. 1, as illustrative of the principles involved in my invention, 4.representsthe source of cathode heating current, shown in this instanceto be a battery, but it may, if desired, be any other source, for example," a. gas flame. is a control rheostat, and 6 is the source of anode Voltage, preferably of several hundred volts. One coil 7 of a telephone transformer is included in the anode circuit, the other coil of which is connected in'the output circuitof the last of a series of audion amplifiers '8 supplying the telephonic current which is to be reproduced. Instead of a direct current source of voltage B between'the anode and cathode as shown in Fig. 1I' can impress upon the lead 9 through a. suitably designed high frequency transformer in place ofthe telehone transformer .an alternating current high voltage, the frequency of which is above the audible limits, for example, if the.

' audion shown at 8 was an oscillion or other This use of radio, or su er-audio, frequencies' possesses certain a vantages in some suitable source of high fre uency current whose amplitudes were. mo ulated in accordance with the telephonic currents to be reproduced into sound, then I find the efl'ect upon the air surrounding the cathode 10 is essentially the same as when simple direct current voltage .is applied therebetween.

cases. It is of course obvious that I can also employ such superimposed modulated high fre uency currents in .combination with the dlrect current source B as shown in Fig.7 1; In. this instance the filament or cathode 1O is 'wound as shown, one terminal of the lead 11 being connected to one end of the filament 10, and wound coincidently therewith is the "anode 12 but; insulated therefrom, one terminal of which. is connected to :the' lead 9.

Fig. 2 shows a sectionalzviewof a repro-- mounting the alternate spirals of anode and cathode in two spiral grooves cut in the face ofithe heat resisting insulatin block 13. To

' ably amplify and direct thesoun thus produced alternate arrangement, wherein instead of a Hat spiral the anode and cathode strips, or

" strip and filament, are wound togetherabout a non-conducting rod 15, which is prefen,

laced'in the axis and approximate focus o? ashort parabolic reflector 14.

' In Fi'. 5 I show a three element repro ducer w erein a third perforated or 'grid manner.

shaped member 16.is introduced between the v cathode and anode spirals. Two such grid members are used, both connected in parallel, to prevent the anode and cathode spirals from being face to face on either side without the interposition of the controlelectrode therebetween. In this three, electrode arrangement the telephonic currents to be reproduced are 'led to the rid and the cathode members, exactly as in t e usual audion amplifier circuit. Such typical circuit is here illustrated. 17 illustrates the input; telephone transformer, the secondary winding of which is connected in the grid-cathode circuit. If desired,a third battery or source .of voltage may be introduced in this gridfilament circuit for the purpose of putting a bias charge upon the grid or control elec trode, as, for example, at the point'18, Fig; 5. In Fig. 6 I illustrate stillanother method for controlling telephonically the instanta neous voltage impressed between the anode and cathode elements of this novel type hf sound reproducer. In this arrangement commonly known as the constant current modulating circuit, my anode 12 and cathod 10 are respectively connected in parallel to the plate and filament electrodes ofamodu, lating audion 19, both devices being thus supplied from a common source of high voltage 20. A large impedance, or inertia, coil 21, is connected in this voltage supply circuit. The telephonic currents to be ampli plied from, the transformer 22 to the circuit of the modulator audion in the ususal By virtue of the highimpedance of the coil 21 high voltage charges are im pressed upon the ionized air space separating. elements 10 and 12 whereby sound waves correspondingto the telephonic-currentimpressed upon the audion grid circuit,vare produced.

As an obvious variation of the above con- '4 llO 'stantcurrent modulatingcirc'uit, a constant voltage circuit may be similarly employed. In this case the open air anode-cathode elements are connected in series with the plate- -filamnt electrodes of the modulating audion,

and with a common source of B voltage.

Then, when the voltage drop across the audion electrodes is causedto vary by the telephonic Volta es impressed upon its grid, a comespongingor rather a reversed charge of the voltage across the open air gap of the sound 'reproducer is"obtaine'd, and sound waves thereby produced. Other systems for mode lating or controlling the voltage or current v acrossthe ionized air gap 'willreadily sug-f gest themselves to ersons skilledin .the art without departing I'0m the spirit" and scope of m invention. -I therefore desire to have.

the descriptions thereof regarded v in --an il lustrative sense rather than in a limiting.

. the illustrations forming part hereof and sense, limited or restricted in any of the details of design, construction, material or instrumentalities employed, but having now set forth the object and nature of my invention and 1 structures embodying the principles .What I claim as new and useful and of my ionizing the air between said cathode and .the medium of an anode in accordance with the sounds to be reproduced.

3. Means for reproducing sound through comprises a long cathode'strip and a long anode stripseparated therefrom, a source of current for said cathode, and means forimpressing accordance with the sounds .to' be reproduced upon the space anode. a

' 4. Means-for reproduclngsound comprisbetween said cathode and i ing a hot cathode and a cold anode separated therefrom,;the effective surface areas of said cathode and .anode being great relative to space f'se'paration therebetween, and means for ionizing the air between said cathode and anode. in-accordance with the sounds to be reproduced.

' tive to the space of se a source of current or sald cathode, and

5. Means for reproducing sound through the medium of an ionized air gap w comprises a cathode and a. cold anode separated therefrom, the effective surface areas of said cathode and anode bein great relameans for impressing ajcurrent' varying in pote'ntialin accordance with the sound to be reproduced upon the space between said cathode and'anode.

6. Means for reproducing soundv comprising a long hot cathode strip and a longtherefrorn, and means between said cathode with the sounds to anode strip'separat'ed for iomzmgjthe air and anode in accordance be reproduced, 'said cathode; and anode being located in the fopen air.

7. Means for-reproducing sound through comprises a long hot cathode strip and a long anode strip sou cc of currentmeans for impressing a for said cathode, and

current varying and do not desire therefore to'be thereof,

through be reproduced, upon the space between ionized air gap which.

a. current varyingun potential in,

aration t erebetween,

. the.medium of an ionized air gap which" separated therefrom, a

otential in accordance with the sounds to e reproduced upon the space between said cathode and anode, said cathode andanode being located in the open air.

v8. Means for, reproducing sound comprisrated therefrom, the effective surface areas of said cathode and anode being great relat ve to space of separation therebetween, and means for, ionizing the air between said cathode .and anode in accordance with the ing a hot cathode and a cold anode sepasounds to be reproduced, said cathode and anode being located in the open air.

.9. Means for reproducing sound through the medium of an ionized air. gap which comprises a cathode and a cold anode sepa rated therefrom, the effective surface areas of said cathode and anode being great relative to the space of se aration therebetween, a source of current or said cathode, and means for impressing a current varying in potential in accordance with the soundto be reproduced upon the spacebetween said cathode and anode.

10. Means for reproducing s ing a hot cathode wound in the form of spiral, a cold anode Wound in a similar spira but separated therefrom throughout its length by a substantially uniform distance," and means for ionizing'the'a'ir between said electrodes in accordance with the sounds to be reproduced.

Y 11. Means for in a hot cathode wound in the form. of a spiral, a cold anode-wound in a similar spiral but separated :therefrom throughout its length by a substantially uniform distance, and both located in the open air, and means for ionizing the air between said electrodes in, accordance with the sounds to be reproduced.

12. Means for reproducing sound comprisin a hot cathode wound in the form of a spiral, a cold anode wound in a similar spiral but separated therefrom throughout its length by a substantially uniformdistance, and1n1eansffor ionizing the air between said electrodes in accordance with the sounds to be reproduced, a loud speaking horn, said electrodes small end of said how. i

13. Means for reproducing sound comprising a hot cathode wound in the form of a spiral, a cold anode wound .in a similar spiral but separated therefrom throughout itsilengthi by a substantially uniform distance, and both located in the open air, and means for ionizing the air between saidelectrodes in accordance with the sounds .to be reproduced, a loud speaking horn, said electrodesbeing located at the small end of said horn.

'. prisinga hot cathode wound mthe form of a spiral, a coldanodenlvound in a similar ound comprisibeing located at the I l reproducing sound .compris- 14. Means for ,reproducin sound, comv spiral but separated therefrom throughout its length by a substantially-uniform disits length bya substantially uniform distance, and both located in the open air, and

means for ionizin the air between saidelectrodes inaccor ance with the sounds to be reproduced, a parabolic horn, said electrodes being located at theapex of said horn;

16. Means for reproducing sound comprising a hot cathode and a cold anode sepa-- rated therefrom, and both exposed to atmos- 1 phere, and means for ioniz1n the air between said cathode and anode in accordance with the sounds to be reproduced through the medium of a third-electrodepositioned between said cathode and anode, but 'sepa- 7 rated therefrom.

' 17. Means for reproducing sound through the medium of an ionized air gap which comprises a cathode and a cold anode separated therefrom and exposed to atmosphere,

a source of current for said cathode, and means for-impressing a current varying in potential in accordance with the sound to be reproduced, upon the space betweensaid cathode and anode, through the medium of athird electrode positioned between said cathode a'ndanode, but separated therefrom.

18. Means for reproducing sound com prising a long cathode strip' and a long anode strip separated therefrom, and means for ionizing the'air'between said cathode and anode in accordance with the sounds to be reproduced through the'medium of a third trve to space of separation t and means for ionizing the air between said electrode positioned between said cathode and anode, but separated therefrom 19. Meansfor reproducing sound comprising a hotca'thode and a cold anode separated therefrom, the effective surface areas of said cathods and anode bein great relaherebetween,

cathode and anode in-accordance with the sounds to be reproduced, through the medium of a third electrode positioned between said cathode and anode,-but separated therefrom. 1'. "20. Means for reproduclng sound through the medium of an ionized air gap which comprises a cathode and a cold anode separated therefrom, the effective surface area of said cathode and anode being great relative to the space of separation therebetween, .a'

source of current for said cathode, \and means for impressing a current varying in potential in accordance with the sound to be reproduced upon the space "between said cathode and anode through the medium of athird electrode positioned between said cathode and anode, but separated therefrom. v I

21. Means for reproducing sound comprising a long cathode strip and a long anodestrip separated therefrom, and means for ionizing the air between said cathode and anodein accordance with the sounds to be reproduced, said cathode and anode being located in the open air, through the medium j of a third electrode positioned between saidcathode and anode, but separated therefrom;

22. Means for reproducing sound through the medium of an ionized air gap which comprises a long cathode strip and a long anode strip separated therefrom, a source of current for said cathode, and means for impressing a current varying in potential in accordance with the sounds to be reproduced upon the space between said cathode andv anode, said cathode and anode being located in the open air, through the medium of a third electrode positioned between said cathode and anode, but separated therefrom.-

'23'. Means for reproducing sound comprising a hot cathode wound in the form of a spiral, a cold anode wound in a similar spiral but separated therefrom throughoutits length by a substantially uniform distance, and means for ionizing the air between said electrodes in' accordance with the sounds to be reproduced through themedium' of a third electrode positioned betweensaid cathode and anode, but separated therefrom. 24. Means for reproducing sound comprising a hot cathode wound in the form of a'spiral, a cold anode wounduin a similar spiral but separated therefrom throughout its length by a substantially uniform distance, and both located in; the open air, and

' means for ionizing the air between said electrodes in accordance with the sounds to be reproduced through the medium of a third electrode positioned between said cathode and anode, but separated therefrom.

In testimony whereof I have hereunto set-- 'my hand on this 24th day of April A. D.,

, LEE' nn .roREs'r. 

